1. Field of the Invention
The present invention relates to an exposure method for producing a hologram mask for exposure to be used in a photolithography process in manufacture of a semiconductor integrated circuit, a liquid crystal display and the like.
2. Description of Related Art
There is a recording method using a phase shift mask, which has a phase-modulation layer called phase shifter, in order to solve an inconvenience that, in a recording method for imaging an exposure pattern of a mask for exposure directly on an object by proximity exposure, lens projection exposure, mirror projection exposure, or the like, resolution of an exposure pattern having a line width of about the same degree of the wavelength of an exposure light is difficult due to a diffraction phenomenon of light (so-called diffraction limit).
In the recording method using such a phase shift mask, if a phase shifter is formed, for example, in one of two close light transmitting portions formed in a phase shift mask to make the phases of lights having transmitted both the light transmitting portions reversed to each other, the diffracted lights are cancelled by each other due to interference with each other in opposite phases, so that the diffraction limit is alleviated to improve the resolution of image formed on the object.
However, in the recording method using a phase shift mask, a lens optical system is used as an imaging optical system, which influences the aberration and a numerical aperture of the lens optical system to give influence on the resolution of an image, thus restricting the resolution of a finally obtained image.
In order to solve such an inconvenience as the resolution of the image is restricted due to the aberration and the numerical aperture of the lens optical system for image-formation, there is proposed a method of forming a pattern having information of an exposure pattern of a phase shift mask, by using a hologram mask with an interference fringe including information of an exposure pattern of a phase shift mask formed thereon and irradiating a laser beam on the hologram mask to form a an image of the light having passed the interference fringe of the hologram mask on an object.
In the recording method using such a hologram mask, whether an optical system such as a lens between the hologram mask and the object is provided or not, an image without aberration in principle and an image of high resolution can be obtained, since a high numerical aperture (NA) is apt to be easily obtained.
However, there was such a problem that the hologram mask is produced by recording the information of the phase shift mask to become an original mask in a hologram material, which makes production of the phase shift mask difficult.